Soil moisture variation due to grass water uptake in shallow slope

Abstract

Shallow landslide is the slope failure phenomenon that frequently occurs in tropical rainforest region such as Malaysia. While fine root distribution for grass with depth is consistent and easily defined, the fine root network plays an important role as geosynthetic mesh by providing apparent enhanced cohesion that increases the strength of the soil. This study is aimed to evaluate the effects of grass on shallow slope stability in terms of soil moisture variation and to develop 1D soil moisture suction due to grass water uptake. The numerical simulation modelling was applied based on the literature review results to obtain the most appropriate condition to replicate the grass water uptake within the soil slope. The transpiration was solely based on six types of grass which have significantly altered the matric suction or moisture variation distribution on an unsaturated soil slope. The types of grass were Axonopus Compressus, Pennisetum Purpureum, Andropogon Gayanus, Brachiaria Humidicola, Melinis Minutiflora and Digitaria Eriantha. The assessment of slope stability due to the influence of six type of grasses induced suction was provided in this research. The length of grass roots are different for all grasses, ranging from 0.3048 m up to 4.000 m. Results of safety factor demonstrated that shallow slope stability is sensitive to pressure head. The factors of safety for all grasses are ranging from 2.8800 until 3.1860. A value which is greater than 1 represents the stability of the slope. This research delivers a strongly belief that Axonopus Compressus grass absorb water way faster from others with factor of safety of 3.0670 and is beneficial in maintaining stability of unsaturated soil.